• Journal of information and communication convergence engineering
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• v.16 no.1
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• pp.17-22
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• 2018

In massive multiple-input multiple-output (MIMO) systems, linear channel estimation algorithms are widely applied owing to their simple structures. However, they may cause pilot contamination, which affects the subsequent data detection performance. Therefore, herein, for an uplink multicell massive multiuser MIMO system, we consider using an alternating projection (AP) for channel estimation to eliminate the effect of pilot contamination and improve the performance of data detection in terms of the bit error rates as well. Even though the AP is nonlinear, it iteratively searches the best solution in only one dimension, and the computational complexity is thus modest. We have analyzed the mean square error with respect to the signal-to-interference ratios for both the cooperative and non-cooperative multicell scenarios. From the simulation results, we observed that the channel estimation results via the AP benefit the following signal detection more than that via the least squares for both the cooperative and non-cooperative multicell scenarios.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.5
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• pp.900-905
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• 2008

I perform bit error rate(BER) analysis of orthogonal frequency division multiplexing(OFDM) systems impaired by both direct current(DC) offset and carrier frequency offset. By analyzing the BER performance for real OFDM systems employing 16-quadrature amplitude modulation(QAM) and pilot symbol estimation, the dependency of BER on the DC offset and carrier frequency offset is quantified and compared to ideal performance. Results show that the magnitude of frequency offset and DC offset are required to be less than 0.01 and 0.007, respectively.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.5
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• pp.165-172
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• 2016

This paper presents an implementation of a live audio streaming system using the Raspberry Pi 3 embedded computer. This system is a live streaming system not file-based streaming. This is a push streaming system which converts the incoming analog audio signal to digital samples and broadcasts them to multiple connected users concurrently. Since the server software is developed in Java language, it can be installed on any other embedded computers without any modification. We concluded that ESCatcher can service live streaming about 60 users concurrently through calculations and experiments, And also we achieved the delay time of a little bit more than 40ms between arrival of audio source and play on the android device.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.6
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• pp.316-323
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• 2004

This paper develops an ADWHM(Advanced Digital Watt-Hour Meter) which integrates and implements the voltage management data record function and the load management data record function in the electronic watt-hour meter. ADWHM is developed based on PIC16F874 which is 8bit micro-controller of RISK type for the easy of programing and maintenance, and electronic power signal processing module is located at front of it to reduce the computing load of processor. Also, a 16kbyte EEPROM is used to record the voltage management data and load management data for a week as well as watt-hour data and USART communication mode is used to transfer data from ADWHM to PC. The accuracy of the voltage and unt measuring for ADWHM is verified by identifying the LCD display values of the ADWHM after the voltage signals of id levels from digital function generator is applied to PT(Potential Transformer) and CT(Current Transformer) output under state which it is separated from real power line. On the its basic functions such as watt-hour data recording function, voltage management data recording function and load management data recording function was verified by showing data for three days among the collected data to PC by RS232C communication from ADWHM which was connected to real power lines for a week.

• Journal of the Optical Society of Korea
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• v.16 no.3
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• pp.313-317
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• 2012

We have evaluated a 1.3 ${\mu}m$ vertical-cavity surface-emitting laser (VCSEL), whose bottom mirror and central active layer were grown by metal organic chemical vapor deposition (MOCVD) and whose top mirror was covered with a dielectric coating, for 10 Gb/s data transmission over single-mode fibers (SMFs). Successful demonstration of error-free transmission of the directly modulated VCSEL signals at data rate of 10 Gb/s over a 10 km-long SMF was achieved for operating temperatures from $20^{\circ}C$ to $60^{\circ}C$ up to bit-error-rate (BER) of $10^{-12}$. The DC bias current and modulation currents are only 7 mA and 6 mA, respectively. The results indicate that the VCSEL is a good low-power consuming optical signal source for 10 GBASE Ethernet applications under controlled environments.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.8
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• pp.1488-1494
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• 2008

This paper is to design and implement a low power noncoherent BFSK receiver intended for future deep space communication using Xilinx System generator. The receiver incorporates a 16 point Fast Fourier Transform(FFT) for symbol detection. The design units of the receiver are digital design for better efficiency and reliability. The receiver functions on one bit data processing and supports main data rate 10kbps. In addition CORDIC algorithm is used for avoiding complex multiplications while computing FFT and multiplication of twiddle factor for low power is substituted by rotators. The design and simulation of the receiver is carried out in Simulink then the Simulink model is translated to the hardware model to implement FPGA using Xilinx System Generator and to verify performance.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.4
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• pp.585-590
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• 2021

This paper proposes a 3-user non-interfering binary pulse amplitude modulation(2PAM) and non-orthogonal multiple access(NOMA) scheme, to improve the bit-error rate(BER) performance of the weakest channel user with the tolerable BER loss of the stronger channel users. First, we design the 3-user non-interfering 2PAM NOMA, and then derive the closed-form expressions for the BERs of the proposed scheme. Numerical results are also presented to demonstrate that the BER of the weakest channel user improves greatly, with the small BER losses of the stronger channel users. As a result, the non-interfering 2PAM could be considered in NOMA of 5G systems.

• ETRI Journal
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• v.34 no.1
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• pp.9-16
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• 2012

Precoding in the multiple-input multiple-output orthogonal frequency division multiplexing system is investigated. In conventional wideband precoding (WBP), only one precoder, obtained from the decomposition of the subcarrier independent channel matrix, is used for all subcarriers. With an investigation of the relationship between the subcarrier independent channel matrix and the temporal/frequency channels, an improved WBP scheme is proposed for practical scenarios in which a part of subcarriers are allocated to a user. The improved WBP scheme is a generalized scheme of which narrow-band precoding and conventional WBP schemes are special modes. Simulation results demonstrate that the improved WBP scheme almost achieves the optimum performance of a single precoder and outperforms the conventional WBP scheme in terms of the bit error ratio and ergodic capacity with slight complexity increase. The largest advantage of the improved WBP scheme on signal-to-noise ratio in simulation results is over 2.1 dB.

• Journal of Broadcast Engineering
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• v.16 no.6
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• pp.977-985
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• 2011

Recent works on multiuser transmission techniques have shown that the linear growth of capacity in single user MIMO system can be translated to the multiuser MIMO scenario as well. In this paper, we propose a method pursuing performance gain of vector perturbation in multiuser downlink systems. Instead of employing maximum number of mobile users for communication, we use small part of them as virtual users for improving reliability of users participating communication. By controlling parameters of virtual users including information and perturbation vector, we obtain considerable improvement in the effective SNR, resulting in large gain in bit error rate performance. Simulation results on the realistic multiuser downlink systems show that the proposed method brings substantial performance gain over the standard vector perturbation with marginal overhead in computations.

• Journal of Advanced Navigation Technology
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• v.8 no.1
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• pp.1-9
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• 2004

In this paper, we have studied the reliable scheme for transmission of digital watermarking-inserted image data through wireless channel. Multimedia data and watermarking data are degraded because of the high BER (Bit Error Rate) and the effect of fading in wireless channel. We adapt the error correction scheme for mitigating the degradation in watermarking data. We have evaluated the error performance of watermarking data modulated by OFDM/16QAM and sent through Rician fading channel. The simulation results show that when error correcting scheme is used the watermarking data can be detected without severe error even though watermarking-inserted image data is suffered from severe damage.